The Biopharmaceutical Classification System (BCS), originally developed by G. Amidon, separates pharmaceuticals for oral administration into four classes depending on their solubility and their absorbability:
Class I—High Permeability, High Solubility
Class II—High Permeability, Low Solubility
Class III—Low Permeability, High Solubility
Class IV—Low Permeability, Low Solubility
Due to the hydrophobic and lipophilic characteristics, the compounds classified as BCS Class II are apt to appear to have spontaneous self-aggregation when mixed with water, resulting in the development of pharmaceutical formulations employing the compound classified as BCS Class II being very limited. However, about 70% of clinically developed drugs are classified as BCS Class II. In order to achieve the expected effect of drugs, the solubility of drugs should be improved to force the dissolved drug into single-molecule form.
Therefore, it is crucial to improve the solubility, absorption, and dissolution of the compounds classified as BCS Class II within the human body, in order to enhance the bio-availability of drugs.